1. Field of the Invention
The present invention relates to a fuel cell system, more specifically to a humidifying structure that humidifies a fuel gas or an oxidation gas, the fuel gas being supplied to a fuel pole of a fuel cell, the oxidation gas being supplied to an oxidant pole thereof
2. Description of Related Art
As eco-friendly electric vehicles, vehicles have recently been developed in which a solid polymer type fuel cell system is mounted. A fuel cell used for the above-described fuel cell system has a plurality of power generation cells in the stack. Each of the power generation cells includes a solid polymer electrolyte membrane having hydrogen ion conductivity, on whose both surfaces anode and cathode carbon electrodes respectively supporting a platinum catalyst are stacked. Gas path forming members formed of lathe-cut metal are respectively stacked on surfaces of the both carbon electrodes, so as to supply a reaction gas thereto. Planar separators are respectively stacked on surfaces of the both gas path forming members.
A hydrogen gas is supplied to the anode electrode as a fuel gas, and air (oxygen gas) is supplied to the cathode electrode as an oxidation gas. The hydrogen gas is ionized on the anode electrode side and transferred to the cathode electrode as the gas permeates the solid polymer electrolyte membrane. On the cathode electrode side, the hydrogen ions react with oxygen and thus generate water. A portion of the generated water permeates the solid polymer electrolyte membrane from the cathode electrode side and flows to the anode electrode side as percolating water. Electrons of the anode electrode are transferred to the cathode electrode through external load. A series of the above-described electrochemical reactions produce electric energy.
In the fuel cell, when the solid polymer electrolyte membrane is dried, permeability of hydrogen ions is lowered. Accordingly, energy conversion efficiency, or power generation efficiency, is lowered. In order to prevent the solid polymer electrolyte membrane from being dried, moisture should be supplied thereto. For this purpose, a unit-type humidifying apparatus is provided to maintain power generation efficiency by humidifying supplied gases, including the fuel gas and the oxidation gas, and thus supplying moisture to the electrolyte membrane.
Related Art 1 discloses a fuel cell humidifying apparatus of the type above. The humidifying apparatus is explained below with reference to FIGS. 7 and 8. Air, which is pressured by a super charger 61, is supplied as an oxidation gas, to an inlet on an oxidant pole side of a fuel cell 60 through an oxidation gas pipe 62. After being used as an oxidant in the fuel cell 60, the air (oxygen) is discharged as an oxidation off-gas along with generated water, from an outlet on the oxidant pole side through an oxidation off-gas pipe 63. A unit-type humidifying apparatus 64, which humidifies the oxidation gas, is connected along the path of the oxidation gas pipe 62 and the oxidation off-gas pipe 63.
The humidifying apparatus 64 has a humidifier 66 in a housing 65, as shown in FIG. 8. The humidifier 66 includes a laterally cylindrical casing 67 and a plurality of hollow fibers 68 (only one of them is illustrated as a thick fiber in the drawing), which are housed in parallel in the casing 67. The oxidation off-gas pipe 63 is connected to both openings of each of the hollow fibers 68. The casing 67 is provided with two openings 69a and 69b. The housing 65 is provided with a compartmented hollow portion 70 corresponding to the opening 69a, and a compartmented hollow portion 71 corresponding to the opening 69b. The oxidation gas pipe 62 is connected to the hollow portions 70 and 71. An oxidation gas path 72 is provided between an internal periphery surface of the casing 67 and an external periphery surface of each of the hollow fibers 68, the oxidation gas path 72 connecting the hollow portions 70 and 71 through the openings 69a and 69b, respectively.
Further, a heating chamber 73 is provided in a middle portion of the housing 65, the heating chamber 73 heating the casing 67 of the humidifier 66. A coolant circulation pipe 74 is connected to the heating chamber 73, the coolant circulation pipe 74 cooling inside the fuel cell 60. A casing 76, which forms a heating chamber 75, is provided in a vicinity of an external periphery of the oxidation off-gas pipe 63 from the fuel cell 60 to the housing 65. The coolant circulation pipe 74 connected to the fuel cell 60 is also connected to the heating chamber 75. Thereby, a coolant, which is heated to a temperature of 120° C., for instance, after having cooled the fuel cell 60, is first directed to the heating chamber 75, in which the coolant heats the oxidation off-gas and generated water flowing in the oxidation off-gas pipe 63. Thereafter, the coolant is supplied from the coolant circulation pipe 74 to the heating chamber 73. The heated coolant heats the path 72 inside the casing 67 of the humidifier 66, and then the heated oxidation gas in the path 72 heats the hollow fiber 68. Further, the generated water flowing in the hollow fiber 68 is heated, and thus evaporated. The water vapor permeates the hollow fiber 68 and is transferred to the path 72. The oxidation gas in the path 72 is humidified by the water vapor, and the humidified oxidation gas is supplied to the fuel cell 60 through the oxidation gas pipe 62.
[Related Art 1] Japanese Patent Laid-open Publication No. 2001-216981
The conventional humidifying apparatus 64 is capable of heating and evaporating the generated water in the hollow fiber 68, by using the heated coolant used for cooling the fuel cell 60 during power generation. Thus, the humidifying apparatus 64 has an advantage requiring no device exclusively for heating. The humidifying apparatus 64, however, has problems as described below. Specifically, the humidifying apparatus 64 has a structure in which the humidifier 66 is housed in the housing 65; the hollow portions 70 and 71 and the heating chamber 73 are provided in the housing 65; the openings 69a and 69b are provided to the casing 67 of the humidifier 66; the oxidation gas path 72 is provided in the casing 67; and the casing 76 is provided to form the heating chamber 75. Consequently, the structure of the humidifying apparatus as a whole is very complex, thus increasing the number of parts, making manufacturing and assembly operations difficult, and preventing reduction in facility cost.
The conventional humidifying apparatus is provided with the heating chamber 73 on the external periphery side of the casing 67, and the path 72 between the internal periphery surface of the casing 67 and the external periphery surface of the hollow fiber 68. Thus, the heated coolant in the heating chamber 73 indirectly heats the water inside the hollow fiber 68. Without the heating chamber 75, the efficiency is lowered in heating and evaporating the generated water in the hollow fiber 68, and thus humidification cannot be performed appropriately.